Hank Bullough admits he's biased on the topic, but it doesn't surprise him one bit that the 3-4 defense is back in vogue.

"It's easier to get linebackers now than it is real good down linemen," the longtime NFL defensive coach said on Friday. "I think you can do a lot more with the 3-4."

Run by at least half the league as late as 1989, the 3-4 -- named for its use of four linebackers and only three down linemen in the base defense -- appeared to be going the way of the drop kick less than a decade ago.

Then, Bill Belichick took over the New England Patriots, began installing elements of the 3-4 and won three Super Bowls in four years.

As it often does, success yielded a trend.

San Diego transitioned to a 3-4 defense in 2004. Dallas and Cleveland followed suit in 2005, and by this past fall, nine teams were playing a base 3-4, including the top-ranked units in Pittsburgh and Baltimore. At least two more teams are expected join the club next season, with experienced 3-4 coordinator Dom Capers calling the defensive shots for the Green Bay Packers and Mike Nolan planning to do the same in Denver.

Next weekend's Super Bowl -- matching the league's longest-running 3-4 defense (Pittsburgh) against the Arizona Cardinals, who run a hybrid defense with many 3-4 elements under coach and former Steelers assistant Ken Whisenhunt -- will serve as a showcase for the sort of dynamic, blitz-heavy attacks that are tempting more and more teams to make the change.

"What's happened is the offenses have become so wide open that coaches are looking for a way to be able to rush three and drop eight in multiple coverages," said John Mackovic, who coached the Kansas City Chiefs from 1983 to 1986, during the scheme's first heyday.

"Also, you can use the zone blitz so much better out of the 3-4. So, if you want to mix up your blitzes and bring an overload blitz to one side or give the quarterback a read that gives him the hard blitz read but you're playing zone behind it, you can do it much easier. In the 4-3 defense, you have to count on those four (linemen) to do a lot."

The 3-4 spreads the responsibility to the linebackers, who can play the run, drop in coverage or rush from a variety of angles. Done correctly, it can disguise blitzes and coverages, isolate offensive linemen one-on-one and create more confusion for quarterbacks than pattern blitzing out of a basic 4-3.

Bullough was among the scheme's pioneers, helping install one of the NFL's first pure 3-4 defenses with Chuck Fairbanks' Patriots in the mid-1970s, around the same time Bum Phillips began running his version with the Houston Oilers. What developed in New England became known as the Bullough/Fairbanks 3-4, a two-gap system Bullough took with him to later stops -- including a stint as Packers defensive coordinator from 1988 to 1991 -- and the grandfather of many modern 3-4 schemes, including Belichick's.

Bullough espoused the scheme in part because it could suit a variety of players and accentuate their strengths. For instance, a player like Pro Football Hall of Fame linebacker Lawrence Taylor could thrive as an edge rusher even though his skills were limited in coverage. Bullough went so far as to name various looks for the players expected to excel in them, such as his Dorsey Defense (after linebacker John Dorsey) and Harris Rover (after linebacker Tim Harris) in Green Bay.

"I think good coaches will coach with the personnel they have, and if you only have one (good) linebacker, you're not going to play a 3-4," said Bullough, who is retired. "But I always felt that you could take a 3-4 and take a guy that was just a wild-eyed, hard player and turn him loose on the quarterback a lot, and you could scheme where you could get some rush from him."

Bullough said he was reluctant to install a 3-4 defense immediately, though, citing the personnel -- a stout nose tackle who can't be single-blocked by a center, ends built more like tackles, big outside linebackers who can rush and/or cover, inside linebackers who can go sideline to sideline -- required to run it effectively.

The scheme has evolved, particularly the zone-blitzing element, but several recent transitions reflect the same challenges.

For every San Diego or Dallas -- two teams that played better on defense in their first seasons with the 3-4 -- there are teams like Nolan's San Francisco 49ers, who ended up playing a hybrid in 2005 and '06 because of personnel shortages and were among the league's worst defenses.

Romeo Crennel's defenses with the Cleveland Browns ranked 26th or worse the past three seasons before he was fired. Another ex-Belichick assistant, Eric Mangini, never had a defense ranked better than 16th in three seasons before the New York Jets let him go. Baltimore slipped from second in yards allowed in 2001 to 22nd in 2002, their first season in the 3-4. Even Belichick's Patriots reverted to the 4-3 during the first Super Bowl run in 2001 and didn't commit fully to the 3-4 until 2003.

Capers vowed in his introductory media conference last week that he's committed to fitting the scheme to the players, not vice versa, and he's shown once before he can lead a quick turnaround. A decade ago, he took over a Jacksonville Jaguars defense that had ranked 25th while playing a 4-3 in 1998. Playing Capers' 3-4 scheme in 1999, the Jaguars improved to No. 4.

"If you've got a bunch of young guys, I think it might be a problem," said longtime NFL coach Jim Mora, whom Capers assisted in the old United States Football League and later with the New Orleans Saints. "But if you've got experienced players, I don't think it will be a problem for them, and I know (the Packers) do."

Mora and Bullough speak highly of Capers' knowledge of the 3-4 scheme, which he honed during a three-year stint as Pittsburgh's defensive coordinator and implemented with expansion teams in Carolina and Houston. Capers began the process this past week of evaluating the existing roster, and any glaring holes can be filled in the coming months through free agency and the draft.

Perhaps the biggest challenge for any coordinator implementing the scheme is selling it to players who have made their living playing in a 4-3, as the Packers have had since 1994.

"When someone says, 'Gee, this is so different, I just don't know,' I've found the truth is they can do a lot of things," Mackovic said. "Certainly, they don't want to be made a fool of -- they want to have a fair fight. So, they want a coach who knows not only what I'm supposed to do but how people might attack us and how to counterattack, and they're counting on those kinds of things. They don't want someone to just draw things up on the board and say, 'OK, here's our defense' and hope it works.

"And in Dom, I think the Packers are getting a coach (who is knowledgeable). I've always thought that he was smart, he knew what to do, he understood what he wanted to do, and he's been around, and I think players will respect that he knows the game."